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Chemical Recovery

Black Liquor Evaporator Scaling Facility.  A bench-scale heated pressure vessel is used to concentrate weak black liquor and determine when soluble scale precipitates. After crystallization filtered samples of the crystals can be collected for chemical analysis and determination of the crystal species.  This information can help diagnose scaling problems in multiple effect evaporators.  During an evaporation run, we monitor the particle size distribution of the precipitates and the boiling point rise. We also have the capability to measure liquor viscosity over a range of solids and temperatures.

Portable Fouling Test Unit (PTFU).   IPST has patented a device consisting essentially of two (or more) annular flow test cells in parallel.  One cell serves as the reference while the other(s) serve as simultaneous test cases.  Each cell is made up of an electrically heated rod within an insulated tube.  Process fluid (e.g. black liquor) flows in the annulus and scale forms on the rod.  By using multiple cells, different conditions, such as Reynolds number or surface temperature, can be compared with respect to scale formation.  Anti-fouling additives can also be evaluated with direct comparison to a reference cell containing no additive.  The PTFU is designed for air transport, and fits in two large Pelican-type cases.  We are pursuing funding to build and test a prototype in a mill.

Combustion Chemistry.  A Laminar Entrained Flow Reactor (LEFR) is used to burn small black liquor particles (100 microns).  The LEFR allows tight control over temperature, residence time, and gas composition.   We have studied sulfur release and recapture, potassium and chloride chemistry, heavy metal release, and NOx/NH3 chemistry.

Model Char Bed Reactor.  A 4-inch square crucible placed within furnace serves as a small scale char bed reactor.  Gas composition and temperature are controlled to mimic the conditions in a recovery boiler bed using the mill’s own liquor to form the char.   Particles in the range of 1 to 100 microns are ejected from the bed and entrained by the rising gases.  Such particles contribute to convective pass fire-side fouling in recovery boilers.  These particles are sampled by deposition on a cooled probe (for SEM) as well as dissolved in a wet scrubber (for chemical analysis).  A visual camera captures the char bed surface activity.    In addition, char bed chemistry and kinetics can be studied. 

Single Drop Reactor. The combustion behavior of black liquors can be measured using this furnace, the data includes the times for drying, devolatilization, and char burning in an environment similar to what is found in recovery boilers.  In addition the swelling behavior of burning particles can be determined.  This fundamental data provides a basis for understanding and modeling the behavior of in-flight combustion of black liquor droplets.

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